In recent years, secondary cells, such as lithium ion secondary cells, of high energy density have been developed as power for electric vehicles and the like. Such secondary cells include a secondary cell configured to house, in a cell case, a flat wound group connected to a current collector member for positive electrode and a current collector member for negative electrode which are arranged at external terminals provided at a case lid.
In order to fix a flat wound group or prevent expansion and contraction of a flat wound group due to charge and discharge, such a secondary cell is configured so that a flat wound group is fixed using an inner wall of a cell case. In some cases, a cell is held from outside by a securing member or the like.
However, in the secondary cell in which the wound group is secured, expansion and contraction of the wound group due to charge and discharge causes discharge of an electrolyte from the wound group (electrolyte depletion). Electrolyte depletion causes reduction in ionic conductance, so that in general, the electrolyte depletion contributes to increase in resistance. In particular, in a secondary cell, such as a lithium ion secondary cell, of high energy density, an electrode has a thick coating and a large current density, and thus, reduction in ionic conductivity in an electrode, caused by such electrolyte depletion, is expected to have a significant influence on increase of DCR. Accordingly, for such a secondary cell, a structure is expected to hold a flat wound group moderately as much as possible.
However, in a secondary cell having such a configuration, a flat wound group being a heavy object is housed in a cell case while being almost suspended from above, so that the flat wound group needs to be held in some way to avoid the risk of breakage of a connection between the flat wound group and a current collector member for positive electrode or a current collector member for negative electrode, due to movement of the flat wound group when vibration or impact is applied to the cell.
PTL 1 discloses a technology about a power storage device having a spacer capable of being arranged on a curved surface of an electrode body to avoid scratch on the electrode body, although its object is different.